This invention relates to a silicone elastomer composition possessing novel crosslinking points, and more particularly, to a silicone elastomer composition possessing two or more organo groups including at least five carbon atoms and a carbon-carbon double bond bonding to a silicon atom via at least one carbon atom as the crosslinking points thereof.
Conventional silicone elastomer compositions have vinyl groups as their crosslinking groups. A shaped article of silicone elastomer, therefore, can be obtained by blending a vinyl group-containing polyorganosiloxane as a base polymer with an organic peroxide as a vulcanizer and molding the obtained blend, or blending with a polyorganohydrogensiloxane and a platinum compound and molding the obtained blend. The organic peroxides available as the aforementioned vulcanizer are divided into two types, acyl type which evolves carboxylic acids and non-acyl type which evolves alcohols.
Among the means of molding silicone elastomer into a desired shape is included hot air vulcanization which is performed in an oxygen-containing atmosphere (hereinafter referred to as "HAV"). When the vulcanization is performed by HAV, there ensures the problem that the surface of the molded product assumes an unvulcanized state unless the vulcanizer is one of only a small number of members selected from the acyl type organic peroxides, such as, for example, 2,4-dichlorobenzoyl peroxide or o-chlorobenzoyl peroxide. The 2,4-dichlorobenzoyl peroxide which is usable in HAV has the disadvantage that 2,4-dichlorobenzoic acid, the product of decomposition thereof, induces the phenomenon of blooming on the surface of the molded elastomer product and seriously impairs its outward appearance. Moreover, the acyl type peroxides have the disadvantage that since these peroxides are transformed by decomposition into carboxylic acids, they have an adverse effect on the heat resistance of silicone elastomer. To avoid this disadvantage, there is adopted a method of subjecting the molded product to a subsequent protracted heating (post-vulcanization).
In contrast, the non-acyl type peroxides which are transformed by decomposition into alcohols fail to give desired vulcanization by HAV, although they do refrain from producing any adverse effect on the silicone elastomer. When a conventional silicone elastomer composition incorporates therein carbon black for the purpose of permitting production of an electroconductive silicone elastomer, the vulcanization of the silicone elastomer composition by HAV cannot be accomplished by either a non-acyl type peroxide or an acyl type peroxide.
As a means of solving the disadvantage described above, there may be cited the method which effects the desired molding by mixing a vinyl group-containing polyorganosiloxane with a polyorganohydrogensiloxane and subjecting the resultant mixture to addition reaction using a platinum compound as a catalyst. Although this method permits vulcanization to be performed by HAV, it has the disadvantage that the elastomer composition incorporating this catalyst is deficient in stability to withstand aging at room temperature and is solidified into elastomer before it is molded into a given shape. Further, the platinum compound used as the catalyst is liable to be poisoned by sulfur or antioxidants which are generally used in most organic rubber composition. When the elastomer composition is molded in the same molding device as is used for organic rubber, the sulfur and antioxidants which remain on the molding device may possibly inactivate the catalyst.
In view of the various disadvantages mentioned above, the desirability of developing a silicone elastomer which can be vulcanized by HAV using a non-acyl type peroxide has found enthusiastic recognition.